Methods for Making High-Protein Greek Yogurt Using Membrane Systems Before and After Fermentation

ABSTRACT

Disclosed are processes for producing high protein, Greek yogurt products. Such processes can include a step of concentrating a skim milk product to produce a protein-enriched milk fraction, which then can be combined with one or more additional milk fractions to form a yogurt base. The yogurt base is inoculated with a yogurt culture and fermented, and at least a portion of the acid whey is removed from the fermented product using a ceramic ultrafiltration membrane system to form the Greek yogurt product.

REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 62/543,414, filed on Aug. 10, 2017, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Yogurt is made by adding bacterial cultures to warm milk, followed byfermentation. During fermentation, lactose in the milk is converted intolactic acid, resulting in a specific texture and flavor. Greek yogurt isa concentrated form of yogurt, in which a part of a water-rich fractionin the form of whey is removed. Greek yogurt, therefore, has higherprotein content than regular yogurt, and since some of the lactose alsogoes with the whey, Greek yogurt also has a lower lactose/carbohydratecontent than regular yogurt.

Traditionally, Greek yogurt was manufactured by fermenting milk into acurd called yogurt, followed by straining the whey from the curd incloth bags. Straining of whey from the curd helped to concentrate thesolids and increase the consistency. The process was slow and manualwith some food safety concerns due to its unhygienic nature.

The present invention is generally directed to improved processes forthe manufacture of high-protein, Greek-style yogurt products.

SUMMARY OF THE INVENTION

This summary is provided to introduce a selection of concepts in asimplified form that are further described herein. This summary is notintended to identify required or essential features of the claimedsubject matter. Nor is this summary intended to be used to limit thescope of the claimed subject matter.

Methods for making a yogurt product are disclosed herein. In accordancewith an aspect of this invention, one such method can comprise (a)concentrating a skim milk product to produce a protein-enriched milkfraction containing from about 3.5 to about 6 wt. % protein, (b)combining the protein-enriched milk fraction with an additional milkfraction to produce a standardized yogurt base containing from about 3.5to about 6 wt. % protein, (c) inoculating the standardized yogurt basewith a yogurt culture and fermenting the inoculated yogurt base toproduce a fermented product, and (d) removing (or separating) at least aportion of acid whey from the fermented product to form the yogurtproduct. In aspects of this invention, the step of removing (orseparating) at least a portion of the acid whey from the fermentedproduct can comprise ultrafiltering the fermented product, for instance,using a ceramic membrane system.

In another aspect, a method for making a yogurt product is disclosed,and in this aspect, the method can comprise (i) concentrating a skimmilk product to produce a standardized yogurt base containing from about3.5 to about 6 wt. % protein, (ii) inoculating the standardized yogurtbase with a yogurt culture and fermenting the inoculated yogurt base toproduce a fermented product, and (iii) removing (or separating) at leasta portion of acid whey from the fermented product to form the yogurtproduct. As above, removing or separating the acid whey can employ aceramic ultrafiltration system.

Unexpectedly, and beneficially, these methods result in an excellentGreek yogurt product, and with the flexibility to increase the proteincontent of the yogurt product up to 20 wt. %, or more. Further, thesemethods can significantly reduce the amount of acid whey (and lactosecontained therein) that must be disposed of.

Both the foregoing summary and the following detailed descriptionprovide examples and are explanatory only. Accordingly, the foregoingsummary and the following detailed description should not be consideredto be restrictive. Further, features or variations can be provided inaddition to those set forth herein. For example, certain aspects can bedirected to various feature combinations and sub-combinations describedin the detailed description.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 presents a schematic flow diagram of a process for producing ayogurt product consistent with an aspect of this invention.

FIG. 2 presents a schematic flow diagram of a process for producing ayogurt product consistent with another aspect of this invention.

DEFINITIONS

To define more clearly the terms used herein, the following definitionsare provided. Unless otherwise indicated, the following definitions areapplicable to this disclosure. If a term is used in this disclosure butis not specifically defined herein, the definition from the IUPACCompendium of Chemical Terminology, 2^(nd) Ed (1997), can be applied, aslong as that definition does not conflict with any other disclosure ordefinition applied herein, or render indefinite or non-enabled any claimto which that definition can be applied. To the extent that anydefinition or usage provided by any document incorporated herein byreference conflicts with the definition or usage provided herein, thedefinition or usage provided herein controls.

Herein, features of the subject matter can be described such that,within particular aspects, a combination of different features can beenvisioned. For each and every aspect and each and every featuredisclosed herein, all combinations that do not detrimentally affect thedesigns, compositions, or processes described herein are contemplatedand can be interchanged, with or without explicit description of theparticular combination. Accordingly, unless explicitly recitedotherwise, any aspect or feature disclosed herein can be combined todescribe inventive designs, compositions, or processes consistent withthe present disclosure.

While compositions and processes are described herein in terms of“comprising” various components or steps, the compositions and methodscan also “consist essentially of” or “consist of” the various componentsor steps, unless stated otherwise.

The terms “a,” “an,” and “the” are intended to include pluralalternatives, e.g., at least one, unless otherwise specified. Forinstance, the disclosure of “a yogurt culture” and “an additional milkfraction” are meant to encompass one, or mixtures or combinations ofmore than one, yogurt culture and additional milk fraction, unlessotherwise specified.

In the disclosed processes, the term “combining” encompasses thecontacting of components in any order, in any manner, and for any lengthof time, unless otherwise specified. For example, the components can becombined by blending or mixing.

Although any methods and materials similar or equivalent to thosedescribed herein can be used in the practice or testing of theinvention, the typical methods and materials are herein described.

Several types of ranges are disclosed in the present invention. When arange of any type is disclosed or claimed, the intent is to disclose orclaim individually each possible number that such a range couldreasonably encompass, including end points of the range as well as anysub-ranges and combinations of sub-ranges encompassed therein. As arepresentative example, the protein content of the yogurt product can bein certain ranges in various aspects of this invention. By a disclosurethat the protein content can be in a range from about 7 to about 25 wt.%, the intent is to recite that the protein content can be any proteincontent within the range and, for example, can be equal to about 7,about 8, about 9, about 10, about 11, about 12, about 13, about 14,about 15, about 16, about 17, about 18, about 19, about 20, about 21,about 22, about 23, about 24, or about 25 wt. %. Additionally, theprotein content can be within any range from about 7 to about 25 wt. %(for example, from about 9 to about 20 wt. %), and this also includesany combination of ranges between about 7 and about 25 wt. % (forexample, the protein content can be in a range from about 7 to about 12wt. %, or from about 15 to about 22 wt. %). Further, in all instances,where “about” a particular value is disclosed, then that value itself isdisclosed. Thus, the disclosure of a protein content from about 7 toabout 25 wt. % also discloses a protein content from 7 to 25 wt. % (forexample, from 9 to 20 wt. %), and this also includes any combination ofranges between 7 and 25 wt. % (for example, the protein content can bein a range from 7 to 12 wt. %, or from 15 to 22 wt. %). Likewise, allother ranges disclosed herein should be interpreted in a manner similarto this example.

The term “about” means that amounts, sizes, formulations, parameters,and other quantities and characteristics are not and need not be exact,but may be approximate including being larger or smaller, as desired,reflecting tolerances, conversion factors, rounding off, measurementerrors, and the like, and other factors known to those of skill in theart. In general, an amount, size, formulation, parameter or otherquantity or characteristic is “about” or “approximate” whether or notexpressly stated to be such. The term “about” also encompasses amountsthat differ due to different equilibrium conditions for a compositionresulting from a particular initial mixture. Whether or not modified bythe term “about,” the claims include equivalents to the quantities. Theterm “about” can mean within 10% of the reported numerical value,preferably within 5% of the reported numerical value.

DETAILED DESCRIPTION OF THE INVENTION

Methods for making yogurt products are disclosed and described herein.These methods can be used to make, for example, high protein, Greekyogurt products with excellent taste and refrigerated shelf-stability,but with reduced levels of acid whey that must be removed to form thefinal yogurt product.

The methods disclosed herein use a specific concentration step to formthe yogurt base prior to fermentation, and a specific acid whey removalstep after fermentation. One potential benefit to these methods is areduction in the fermentation time needed to form the fermented product.Another potential benefit is a more efficient removal of acid whey fromthe fermented product. Whey can be removed from the fermented product bymechanical centrifugal separators or by filtering through specialmembranes. Mechanical means can perform the separation based ondifferences in density. Centrifugal means can perform mechanicalseparation by applying centrifugal force. Use of mechanical separatorsto remove whey can result in the loss of some whey proteins, and puts alimitation on the protein content that can be achieved.

Filtration technologies (e.g., microfiltration, ultrafiltration,nanofiltration, and reverse osmosis) separate or concentrate componentsin mixtures—such as milk—by passing the mixture through a membranesystem (or selective barrier) under a suitable pressure. Theconcentration/separation is, therefore, based on molecular size. Thestream that is retained on by the membrane is called the retentate (orconcentrate). The stream that passes through the pores of the membraneis called the permeate. As an example, the pore size of ultrafiltrationmembranes typically varies from 0.01 to 0.1 microns. In the dairyindustry, the ultrafiltration membranes often are identified based onmolecular weight cut-off (MWCO), rather than pore size. The molecularweight cut-off for ultrafiltration membranes can vary from 1000-100,000Daltons.

As it pertains to the methods disclosed herein, and beneficially,ultrafiltration (and other membrane technologies) can be used toconcentrate protein in the retentate to produce a higher-protein yogurtbase, and if desired, a higher-protein yogurt product. Alsobeneficially, ultrafiltration (and other membrane technologies) can beused to remove the acid whey from the fermented product to result in theyogurt product. The amount of acid whey that must be removed can bereduced due to the higher-protein content of the yogurt base.

Reconstituted milk protein powders can be used to increase the proteincontent in Greek yogurt, but that results in poor taste of the finalproduct, due to the longer fermentation time from yogurt bacteriainoculation until the yogurt curd is formed, and due to nature of dryprotein powders. Moreover, the solubility of milk protein powders hasits own challenges. Further, simply concentrating milk to the Greekyogurt solids level, followed by bacterial inoculation of theconcentrated milk to get the desired acidity of Greek yogurt, results inlong fermentation time and the poor product taste. It is believed thatthe methods disclosed herein overcome these deficiencies.

Methods for Making Yogurt Products

In one aspect, a method for making a yogurt product is provided, and inthis aspect, the method can comprise (or consist essentially of, orconsist of) (a) concentrating a skim milk product to produce aprotein-enriched milk fraction containing from about 3.5 to about 6 wt.% protein, (b) combining the protein-enriched milk fraction with anadditional milk fraction to produce a standardized yogurt basecontaining from about 3.5 to about 6 wt. % protein, (c) inoculating thestandardized yogurt base with a yogurt culture and fermenting theinoculated yogurt base to produce a fermented product, and (d) removing(or separating) at least a portion of acid whey from the fermentedproduct to form the yogurt product. In another aspect, a method formaking a yogurt product is provided, and in this aspect, the method cancomprise (or consist essentially of, or consist of) (i) concentrating askim milk product to produce a standardized yogurt base containing fromabout 3.5 to about 6 wt. % protein, (ii) inoculating the standardizedyogurt base with a yogurt culture and fermenting the inoculated yogurtbase to produce a fermented product, and (iii) removing (or separating)at least a portion of acid whey from the fermented product to form theyogurt product.

Generally, the features of the methods (e.g., the characteristics of theskim milk product or yogurt base, the amount and type of the yogurtculture, the techniques used for the concentrating and removing steps,the amount of acid whey removed, and the characteristics of the yogurtproduct, among others) are independently described herein and thesefeatures can be combined in any combination to further describe thedisclosed methods. Moreover, other process steps can be conductedbefore, during, and/or after any of the steps listed in the disclosedmethods, unless stated otherwise. Additionally, the yogurt products(e.g., high protein Greek yogurts, ready for consumption) produced inaccordance with any of the disclosed methods are within the scope ofthis disclosure and are encompassed herein.

The skim milk product in step (a) and step (i) can have suitable amountsof lactose (or milk sugar), protein, fat, minerals, and solids. Forexample, the skim milk product can have less than or equal to about 0.5wt. % fat, less than or equal to about 0.25 wt. % fat, or less than orequal to about 0.15 wt. % fat. The protein content of the skim milkproduct often ranges from about 3 to about 4 wt. %, the lactose contentoften ranges from about 4 to about 6 wt. %, the mineral content oftenranges from about 0.5 to about 0.9 wt. %, and the solids content oftenranges from about 8 to about 11 wt. %, although other appropriate rangesfor these milk components are readily apparent from this disclosure.

Before step (a) and step (i), the skim milk product can be producedusing any suitable technique, an example of which is separating (e.g.,centrifugally separating) a fresh or raw milk product into the skim milkproduct and cream. The fresh or raw milk product can be cow's milk,which contains approximately 87 wt. % water, 3-4 wt. % protein, 4-5 wt.% carbohydrates/lactose, 3-4 wt. % fat, and 0.3-0.8 wt. % minerals. Whenthe fresh or raw milk product is separated into the skim milk productand cream, the cream fraction typically contains high levels of fat(e.g., 20-50 wt. % fat, or 30-50 wt. % fat) and solids (e.g., 30-60 wt.%, or 40-55 wt. %), and often contains approximately 1.5-3.5 wt. %protein, 2-5 wt. % lactose, and 0.2-0.9 wt. % minerals, although notlimited thereto.

In step (a), the skim milk product can be concentrated to produce aprotein-enriched milk fraction containing from about 3.5 to about 6 wt.% protein, while in step (i) the skim milk product can be concentratedto produce a standardized yogurt base containing from about 3.5 to about6 wt. % protein. While not being limited thereto, the concentrationsteps can be conducted at a temperature in a range from about 3 to about15° C., and more often from about 3 to about 10° C., or from about 5 toabout 8° C. In one aspect, the steps of concentrating the skim milkproduct can comprise ultrafiltering the skim milk product. For instance,the skim milk product can be ultrafiltered using a polymeric membranesystem. The polymeric membrane system can be configured with pore sizessuch that the materials having molecular weights greater than about1,000 Daltons, greater than about 5,000 Daltons, or greater than about10,000 Daltons, are retained, while lower molecular weight species passthrough. In some aspects, ultrafiltration utilizes a membrane systemhaving pore sizes in a range from about 0.01 to about 0.1 μm, andoperating pressures typically in the 45-150 psig range.

In another aspect, the steps of concentrating the skim milk product cancomprise nanofiltering the skim milk product. Generally, nanofiltrationutilizes a membrane system having pore sizes in a range from about 0.001to about 0.01 μm. Operating pressures typically are in the 150-450 psigrange.

In another aspect, the steps of concentrating the skim milk product cancomprise microfiltering the skim milk product. Generally,microfiltration utilizes a membrane system having pore sizes in a rangefrom about 0.1 to about 0.2 μm. Operating pressures typically are belowabout 75 psig.

In another aspect, the steps of concentrating the skim milk product cancomprise diafiltering the skim milk product. Generally, thediafiltration step is performed using ultrafiltration membranes, such asdescribed herein: materials with molecular weights greater than about1,000 Daltons, greater than about 5,000 Daltons, or greater than about10,000 Daltons, typically are retained, while lower molecular weightspecies pass through. The membrane system can have pore sizes in a rangefrom about 0.01 to about 0.1 μm, and operating pressures typically inthe 45-150 psig range. Often, diafiltering the skim milk product cancomprise diafiltering a mixture of the skim milk product and water, butis not limited thereto, and at any suitable weight ratio of the water tothe skim milk product (e.g., from about 0.1:1 to about 1:1), and at anysuitable concentration factor (e.g., from about 1.2 to about 5).

In yet another aspect, the steps of concentrating the skim milk productcan comprise subjecting the skim milk product to reverse osmosis.Reverse osmosis is a tight filtration process in which substantially allthe milk components are retained, and only water passes through.Generally, reverse osmosis utilizes a membrane system having pore sizesof less than or equal to about 0.001 μm. Operating pressures typicallyare in the 450-600 psig range.

In yet another aspect, the steps of concentrating the skim milk productcan comprise subjecting the skim milk product to forward osmosis.Forward osmosis is typically performed at lower pressures than standardreverse osmosis, and utilizes a semi-permeable membrane system havingpore sizes such that water passes through, while other materials (e.g.,proteins, fats, lactose or other sugars, and minerals) do not. Operatingpressures typically range from about 0 psig (atmospheric pressure) toabout 50 psig, from about 0 psig to about 10 psig, from about 1 psig toabout 50 psig, from about 1 psig to about 30 psig, from about 1 psig toabout 10 psig, from about 10 psig to about 30 psig, from about 15 toabout 25 psig, and the like. While not being limited thereto, forwardosmosis membrane systems have a molecular weight cutoff of much lessthan 100 Da and, therefore, components other than water can beconcentrated in the forward osmosis process. Generally, forward osmosiscomprises a membrane system having pore sizes of less than or equal toabout 0.001 μm. Any suitable draw solution that has a higherconcentration of solutes or ions than the solution from which water isto be drawn through a semipermeable membrane can be used for the forwardosmosis step.

In still another aspect, the steps of concentrating the skim milkproduct can comprise condensing the skim milk product under reducedpressure. Reduced pressure encompasses any suitable sub-atmosphericpressure, and typically involves the use of a vacuum system orapparatus. Elevated temperatures can be employed during the condensingstep, but this is not a requirement.

Regardless of the concentrating technique that is utilized, the proteincontent of the protein-enriched milk fraction (step (a)) and thestandardized yogurt base (step (i)) increases, as compared to that ofthe skim milk product, and generally falls within the range from about3.5 to about 6 wt. % protein. In some aspects, the amount of protein inthe protein-enriched milk fraction (step (a)) and the standardizedyogurt base (step (i)), independently, can be in a range from about 3.8to about 5.5 wt. % protein; alternatively, from about 3.7 to about 5 wt.% protein; alternatively, from about 3.7 to about 4.5 wt. % protein;alternatively, from about 4 to about 5.2 wt. % protein; oralternatively, from about 4.1 to about 4.8 wt. % protein. Otherappropriate ranges for the amount of protein in the protein-enrichedmilk fraction (step (a)) and/or in the standardized yogurt base (step(i)) are readily apparent from this disclosure.

Likewise, the percent solids of the protein-enriched milk fraction (step(a)) and the standardized yogurt base (step (i)) can increase, ascompared to that of the skim milk product, due to the concentrationprocess. The solids contents can fall within a range from about 9 toabout 20 wt. %, from about 9.5 to about 15 wt. %, from about 10 to about14 wt. %, or from about 10 to about 12 wt. %, although not being limitedthereto. The protein-enriched milk fraction (step (a)) and thestandardized yogurt base (step (i)) often can contain less than or equalto about 0.5 wt. % fat, less than or equal to about 0.25 wt. % fat, orless than or equal to about 0.15 wt. % fat, as well as a typical lactosecontent from about 4 to about 6 wt. %, and a typical mineral contentfrom about 0.7 to about 1.3 wt. %, or from about 0.85 to about 1.2 wt.%.

In step (b) of the first method for making a yogurt product, theprotein-enriched milk fraction can be combined with an additional milkfraction to produce a standardized yogurt base containing from about 3.5to about 6 wt. % protein. The standardized yogurt base of step (b) canhave generally the same respective amounts of protein, fat, lactose,minerals, and solids as that of the standardized yogurt base in step(i). For example, the standardized yogurt base in step (b) can containfrom about 3.5 to about 6 wt. % protein, from about 3.8 to about 5.5 wt.% protein, from about 3.7 to about 5 wt. % protein, from about 3.7 toabout 4.5 wt. % protein, from about 4 to about 5.2 wt. % protein, orfrom about 4.1 to about 4.8 wt. % protein, and have a solids contentfrom about 9 to about 15 wt. %, from about 9.5 to about 14 wt. %, fromabout 10 to about 14 wt. %, or from about 10 to about 12 wt. %, althoughother appropriate ranges are readily apparent from this disclosure.

Any suitable additional milk fraction can be combined with theprotein-enriched milk fraction to result in the standardized yogurtbase. Illustrative additional milk fractions can include, but are notlimited to, cream, skim milk, a lactose-rich fraction, a mineral-richfraction, water, and the like, as well as mixtures or combinationsthereof. In some aspects, the additional milk fraction can comprise skimmilk, a mineral-rich fraction, or both. As an example, cream can beadded to increase the fat and solids content of the standardized yogurtbase (e.g., up to approximately 1-5 wt. % or 2-4 wt. % fat, and up toapproximately 12-17 wt. % or 12-16 wt. % solids, although not beinglimited thereto). As another example, a lactose-rich fraction can beadded to increase the sugar content of the standardized yogurt base. Asyet another example, a mineral-rich fraction can be added to increasethe mineral content of the standardized yogurt base. As still anotherexample, skim milk can be added to increase the mineral content and/orsugar content of the standardized yogurt base. One or more than oneadditional milk fraction can be combined with, in any relativeproportion, the protein-enriched milk fraction to produce thestandardized yogurt base in step (b). A “component-rich fraction” ismeant to encompass any fraction containing at least 15% more of acomponent of milk (protein, lactose/sugar, fat, minerals) than thatfound in cow's milk. For instance, a lactose-rich fraction often cancontain from about 6 to about 20 wt. % sugar (i.e., in any form, such aslactose, glucose, galactose, etc.), from about 6 to about 18 wt. %sugar, or from about 7 to about 16 wt. % sugar. A mineral-rich fractioncan contain from about 1 to about 20 wt. % minerals, from about 1 toabout 10 wt. % minerals, or from about 1.5 to about 8 wt. % minerals. Afat-rich fraction (e.g., cream) often can contain from about 8 to about50 wt. % fat, from about 20 to about 50 wt. % fat, or from about 30 toabout 45 wt. % fat.

These component-rich milk fractions can be produced by any techniqueknown to those of skill in the art. While not limited thereto, thecomponent-rich milk fraction (or milk fractions) can be produced by amembrane filtration process, such as disclosed in U.S. Pat. Nos.7,169,428, 9,510,606, and 9,538,770, which are incorporated herein byreference in their entirety. For example, fresh or raw milk can befractionated into skim milk and cream (fat-rich fraction) by centrifugalseparators. The skim milk can be fractionated via combinations ofmicrofiltration, ultrafiltration, nanofiltration, and reverse osmosis(or forward osmosis) into a protein-rich fraction, a lactose-richfraction, a mineral/flavor-rich fraction, and a milk water fraction.Additionally or alternatively, the component-rich milk fraction (or milkfractions) can be produced by a process comprising mixing water and apowder ingredient (e.g., protein powder, lactose powder, mineral powder,etc.).

In one aspect of this invention, the skim milk product in step (a) canbe concentrated using ultrafiltration, and the resulting UF retentatecan be combined with skim milk, in any suitable proportion, to form thestandardized yogurt base in step (b).

In another aspect, the skim milk product in step (a) can be concentratedusing diafiltration (with an ultrafiltration membrane), and theresulting DF retentate can be combined with skim milk, in any suitableproportion, to form the standardized yogurt base in step (b).

In another aspect, the skim milk product in step (a) can be concentratedusing microfiltration, and the resulting MF retentate can be combinedwith skim milk, in any suitable proportion, to form the standardizedyogurt base in step (b).

In yet another aspect, the skim milk product in step (a) can beconcentrated using ultrafiltration, and the resulting UF retentate canbe combined with a mineral-rich fraction, in any suitable proportion, toform the standardized yogurt base in step (b). The mineral-rich fractioncan be produced using reverse osmosis, forward osmosis, or othersuitable technique.

In still another aspect, the skim milk product in step (a) can beconcentrated using diafiltration (with an ultrafiltration membrane), andthe resulting DF retentate can be combined with a mineral-rich fraction,in any suitable proportion, to form the standardized yogurt base in step(b). The mineral-rich fraction can be produced using reverse osmosis,forward osmosis, or other suitable technique.

While not limited thereto, the standardized yogurt base can contain fromabout 1100 to about 1800 ppm (by weight) of calcium in one aspect, fromabout 1200 to about 1800 ppm in another aspect, and from about 1200 toabout 1600 ppm in yet another aspect (e.g., from about 1300 to about1400 ppm). Likewise, the standardized yogurt base can contain from about800 to about 1200 ppm phosphorus in one aspect, from about 850 to about1150 ppm in another aspect, and from about 800 to about 1100 ppm in yetanother aspect (e.g., from about 940 to about 980 ppm). The standardizedyogurt base can be characterized by a weight ratio of calcium to proteinthat can fall within a range from about 0.02 to about 0.04, from about0.025 to about 0.035 ppm, or from about 0.028 to about 0.033 (e.g., fromabout 0.029 to about 0.032). Additionally or alternatively, thestandardized yogurt base can be characterized by a weight ratio ofphosphorus to protein often falling in a range from about 0.013 to about0.033, from about 0.015 to about 0.03 ppm, or from about 0.018 to about0.025 (e.g., from about 0.02 to about 0.023).

The pH of the standardized yogurt base is generally neutral. Forinstance, the pH of the standardized yogurt based can be in a range fromabout 6.3 to about 7.3 in one aspect, from about 6.6 to about 6.9 inanother aspect, and from about 6.7 to about 7 in yet another aspect.Beneficially, the standardized yogurt base can have a calcium tophosphorus ratio and a pH level that are similar to that of the startingmaterial (e.g., the skim milk product).

Optionally, the disclosed methods can further comprise a step ofpasteurizing the standardized yogurt base between step (b) and step (c),or between step (i) and step (ii). Any suitable pasteurizationconditions can be used, such as conducting the pasteurization step at atemperature in a range from about 80 to about 95° C. for a time periodin a range from about 2 to about 15 minutes; or alternatively, at atemperature of approximately 90° C. for a time period in a range fromabout 5 to about 7 minutes.

In step (c) and step (ii), the yogurt base can be inoculated (orcontacted or combined) with a yogurt culture and the inoculated yogurtbase can be fermented to produce a fermented product. The yogurt basegenerally is inoculated and/or fermented at an elevated temperature. Inone aspect, the yogurt base can be inoculated and/or fermented at atemperature in a range from about 20 to about 45° C., while in anotheraspect, the yogurt base can be inoculated and/or fermented at atemperature in a range from about 35 to about 45° C., and in yet anotheraspect, the yogurt base can be inoculated and/or fermented at atemperature in a range from about 40 to about 45° C. Other appropriateinoculation and/or fermentation temperatures are readily apparent fromthis disclosure.

The amount and type of the yogurt culture used can vary depending uponthe desired attributes of the final yogurt product as well as thecharacteristics of the yogurt base. While not being limited thereto, theamount of the yogurt culture can range from about 0.0001 to about 3 wt.%, from about 0.0005 to about 0.05 wt. %, from about 0.0001 to about0.01 wt. %, or from about 0.0005 to about 0.01 wt. %, based on theweight of the standardized yogurt base. Other appropriate ranges for theamount of the yogurt culture added to the yogurt base are readilyapparent from this disclosure.

The form of the yogurt culture is not particularly limited; the yogurtculture can be bulk, freeze dried, or frozen, and mixtures orcombinations can be used as well. Typical yogurt cultures that can beused include, but are not limited to, Lactobacillus bulgaricus,Streptococcus thermophilus, Lactobacillus acidophillus, Lactobacilluscasei, Lactococcus lactis, Lactococcus cremoris, Latobacillus plantarum,Bifidobacterium, Leuconostoc, and the like, as well as any combinationthereof. In some aspects, the yogurt culture can comprise Lactobacillusbulgaricus, Streptococcus thermophilus, or a combination thereof.

As would be readily recognized by those of skill in the art, anysuitable vessel can be used for forming the fermented product, and suchcan be accomplished batchwise or continuously. As an example, thefermentation step can be conducted in a tank, a silo, or a vat. Anysuitable period of time can be used, and this can depend upon thetemperature and the amount of the yogurt culture, amongst othervariables. Generally, the inoculated yogurt base can be fermented for atime period in a range from about 1 to about 18 hours, from about 2 toabout 8 hours, or from about 3 to about 7 hours.

Typically, the inoculated yogurt base is fermented until the pH of thefermented product has reached a certain pH range. In some aspects, forexample, the targeted pH can be in a range from about 4.3 to about 4.8,from about 4.4 to about 4.8, from about 4.4 to about 4.7, from about 4.5to about 4.8, from about 4.5 to about 4.7, from about 4.6 to about 4.8,or from about 4.6 to about 4.7. Other appropriate ranges for the pH ofthe fermented product are readily apparent from this disclosure.

Optionally, the disclosed methods can further comprise a step ofagitating the fermented product between step (c) and step (d), andbetween step (ii) and step (iii). Often, this step can be referred to asbreaking of the curd. Additionally or alternatively, the disclosedmethods can further comprise a step of heat treating the fermentedproduct between step (c) and step (d), and between step (ii) and step(iii). The optional heat treating step can be performed after theagitation step and at any suitable combination of temperature and time,such as at a temperature in a range from about 55 to about 65° C. for atime period in a range from about 1 to about 3 minutes.

In step (d) and step (iii), at least a portion of acid whey from thefermented product is removed to form the yogurt product. In one aspect,removing at least a portion of the acid whey from the fermented productcan comprise ultrafiltering the fermented product. While not beinglimited thereto, ultrafiltration of the fermented product can beconducted at a temperature in a range from about 35 to about 55° C.;alternatively, from about 40 to about 60° C.; or alternatively, fromabout 45 to about 55° C. In these acid whey removal steps, the fermentedproduct can be ultrafiltered using a ceramic membrane system. Theceramic membrane system can be configured with pore sizes of less thanor equal to about 0.1 μm, such that the acid whey passes through thepores, and the yogurt product is retained. While not wishing to be boundby the following theory, it is believed that a ceramic membrane systemis superior to a polymeric membrane system at this stage of the process,in which a higher viscosity product (the fermented product) isultrafiltered to retain the yogurt product. Further, a ceramic membranesystem can withstand higher operating temperatures, has more cleaningoptions (pH range from acid to alkaline, as well as hot watersterilization at 80-90° C. for 30 to 90 min), and fouling/scale can bemore easily removed by exposure to elevated temperatures.

In another aspect, the steps of removing at least a portion of the acidwhey can be achieved by nanofiltering the fermented product. Generally,nanofiltration utilizes a membrane system having pore sizes in a rangefrom about 0.001 to about 0.01 μm, and temperatures ranging from about15 to about 45° C. often can used.

In another aspect, the steps of removing at least a portion of the acidwhey can be achieved by microfiltering the fermented product. Generally,microfiltration utilizes a membrane system having pore sizes in a rangefrom about 0.1 to about 0.2 μm, and temperatures ranging from about 35to about 55° C. often can used.

In yet another aspect, the steps of removing at least a portion of theacid whey can be achieved by subjecting the fermented product to reverseosmosis. Generally, reverse osmosis utilizes a membrane system havingpore sizes of less than or equal to about 0.001 μm, and temperaturesranging from about 15 to about 45° C. often can used.

In still another aspect, the steps of removing at least a portion of theacid whey can be achieved by subjecting the fermented product to amechanical separation process. Often, the mechanical separation processcan comprise centrifugal separation, but other suitable separationsprocesses can be used.

Regardless of the acid whey removal technique that is utilized, a largemajority of the acid whey is removed from the fermented product. Inaccordance with aspects of this invention, at least about 90 wt. %, atleast about 92 wt. %, at least about 95 wt. %, at least about 98 wt. %,or at least about 99 wt. %, of the acid whey present in the fermentedproduct is removed in step (d) or step (iii). The acid whey materialthat is removed has a very low solids content, typically characterizedby a solids content of less than about 8 wt. %, less than about 7 wt. %,or less than about 6.5 wt. %.

Depending upon the characteristics of the yogurt base, the relativeamounts of the yogurt product and the acid whey can vary. In one aspect,the weight ratio of the yogurt product to the acid whey in the fermentedproduct can be in a range from about 35:65 to about 70:30. In anotheraspect, the weight ratio of the yogurt product to the acid whey in thefermented product can be in a range from about 40:60 to about 70:30. Inyet another aspect, the weight ratio of the yogurt product to the acidwhey in the fermented product can be in a range from about 45:55 toabout 65:35. Other ranges for the weight ratio of the yogurt product tothe acid whey in the fermented product are readily apparent from thisdisclosure.

The disclosed methods can further comprise a step of packaging theyogurt product in a container. Optionally, this packaging step can beperformed aseptically, using any suitable aseptic filling/packagingsystem.

In further aspects of this invention, the disclosed methods can furthercomprise a step of combining the yogurt product and any suitableingredient, and packaging in a container. Non-limiting examples of suchingredients can include a sugar/sweetener, a flavorant, a preservative(e.g., to prevent yeast or mold growth), a stabilizer, an emulsifier, aprebiotic substance, a special probiotic bacteria, a vitamin, a mineral,an omega 3 fatty acid, a phyto-sterol, an antioxidant, or a colorant,and the like, as well as any mixture or combination thereof.

Prior to packaging, the disclosed methods can further comprise a step ofcooling to a suitable temperature, such as in a range from about 15 toabout 25° C., from about 15 to about 21° C., or from about 15 to about20° C. Also prior to packaging, or after packaging in a suitablecontainer, the yogurt product can be heat treated for shelf-stability.Any suitable container can be used to package the yogurt product, suchas might be used for the distribution and/or sale of yogurt products ina retail outlet. Illustrative and non-limiting examples of typicalcontainers include a cup, a bottle, a bag, or a pouch, and the like. Thecontainer can be made from any suitable material, such as glass, metal,plastics, and the like, as well as combinations thereof.

The packaged yogurt product generally is stored at refrigeratedconditions, such as in a range from about 2° C. to about 10° C., or fromabout 1 to about 5° C. Under refrigerated conditions (2-10° C., or 1-5°C.), the yogurt product can be shelf-stable for a time period in a rangefrom about 30 to about 90 days; alternatively, shelf-stable for a timeperiod of from about 30 to about 60 days; or alternatively, shelf-stablefor a time period of from about 30 to about 45 days.

If desired, the methods disclosed herein can further comprise atreatment step to increase the shelf-stability of the yogurt product.Such treatment steps can include, but are not limited to,pasteurization, ultra-high temperature (UHT) sterilization, highpressure processing (HPP), and the like, as well as combinationsthereof. After such treatment, the yogurt product can be shelf-stablewithout refrigeration (at a temperature from about 20° C. to about 25°C.) for a time period in a range from about 7 to about 180 days, fromabout 7 to about 120 days, from about 14 to about 120 days, or fromabout 30 to about 150 days.

The yogurt products of the methods disclosed herein typically cancontain a relatively high amount of protein. In one aspect, the yogurtproduct can contain from about 7 to about 25 wt. % protein (e.g., fromabout 7 to about 12 wt. % protein). In another aspect, the yogurtproduct can contain from about 9 to about 20 wt. % protein (e.g., fromabout 9 to about 12 wt. % protein). In yet another aspect, the yogurtproduct can contain from about 8 to about 13 wt. % protein (e.g., fromabout 8 to about 10 wt. % protein). In still another aspect, the yogurtproduct can contain from about 12 to about 20 wt. % protein.

The lactose content of the yogurt product is not limited to anyparticular range, but often, the yogurt product can contain from about0.5 to about 3 wt. % lactose, or from about 1 to about 2 wt. % lactose.Additionally or alternatively, the yogurt product beneficially can havea relatively high weight ratio of protein to lactose (protein:lactose),such as greater than or equal to about 4:1, greater than or equal toabout 5:1, greater than or equal to about 6:1, greater than or equal toabout 8:1, or greater than or equal to about 10:1. At high levels ofprotein content (e.g., 15-20 wt. %), the amount of lactose can be lessthan 1 wt. % (and approach zero); therefore, the protein:lactose ratiocan be greater than 50:1, or greater than 100:1, in some aspects of thisinvention. In the examples that follow, the protein:lactose ratio is inthe 5:1 to 6:1 range.

Further, the yogurt product can be characterized by a solids content ina range from about 10 to about 30 wt. %, from about 12 to about 20 wt.%, from about 11 to about 19 wt. %, or from about 13 to about 16 wt. %.Additionally or alternatively, the yogurt product can be characterizedby a titratable acidity (% lactic acid) in a range from about 0.75 toabout 2%, or from about 1 to about 1.5%. Additionally or alternatively,the yogurt product can be characterized by a fat content of less than orequal to about 0.7 wt. % fat, less than or equal to about 0.5 wt. % fat,or less than or equal to about 0.3 wt. % fat, or a fat content in arange from about 1 to about 8 wt. % fat, or from about 2 to about 7 wt.% fat. Additionally or alternatively, the yogurt product can becharacterized by a mineral content from about 0.8 to about 2 wt. %, orfrom about 0.9 to about 1.5 wt. %.

An illustrative and non-limiting example of a suitable method for makinga yogurt product consistent with aspects of this invention is shown inFIG. 1. First, fresh whole milk is separated into cream and a skim milkproduct. The skim milk product is then subjected to ultrafiltration,such as via a polymeric membrane system, as described herein, resultingin a retentate often referred to as the protein-enriched milk fraction.Additional milk fractions, such as cream, then can be combined with theprotein-enriched milk fraction, to form a standardized yogurt base withthe desired amounts of the respective milk components (e.g., protein,fat, lactose, and minerals).

In FIG. 1, the yogurt base is pasteurized and then cooled to atemperature of 40-45° C., followed by inoculating the yogurt base with ayogurt culture, and incubating (or fermenting) the inoculated yogurtbase until a target pH has been reached, for example, a pH of 4.6. Theresulting fermented product is subjected to agitation to break the curd,followed by a heat treatment step, typically in the 55-65° C. range. Thefermented product is then subjected to ultrafiltration, such as via aceramic membrane system, as described herein, resulting in a retentateoften referred to as the yogurt product, and a permeate that containsthe acid whey from the fermented product.

Flavor, sugar/sweetener, and stabilizer ingredients are combined withthe yogurt product in FIG. 1, followed by cooling to 20-25° C., andpackaging (e.g., aseptically) in a suitable container, such as a bottle,cup, or bag. The packaged yogurt product is generally stored atrefrigerated conditions, often in the 1-5° C. range.

Another illustrative and non-limiting example of a suitable method formaking a yogurt product consistent with aspects of this invention isshown in FIG. 2. The steps in FIG. 2 are the same as those in FIG. 1,except that the fermented product is subjected to a mechanicalseparation step (such as centrifugal separation, instead ofultrafiltration with a ceramic membrane system), resulting in aretentate often referred to as the yogurt product, and a permeate thatcontains the acid whey from the fermented product.

Examples

The invention is further illustrated by the following examples, whichare not to be construed in any way as imposing limitations to the scopeof this invention. Various other aspects, modifications, and equivalentsthereof which, after reading the description herein, can suggestthemselves to one of ordinary skill in the art without departing fromthe spirit of the present invention or the scope of the appended claims.

Total solids (wt. %) was determined in accordance with procedure SMEDP15.10 C by CEM Turbo Solids and Moisture Analyzer (CEM Corporation,Matthews, N.C.). Ash is the residue remaining after ignition in asuitable apparatus at 550° C. to a constant weight; such treatment at550° C. typically eliminates all organic matter, with the remainingmaterial being primarily minerals (Standard Methods for the examinationof dairy products, 17^(th) edition (2004), American Public HealthAssociation, Washington D.C.). The ash test was performed by using aPhoenix (CEM Microwave Furnace), which heated the samples at 550° C. for30 min. The ash content was determined in wt. %. The mineral content (inwt. %) is generally similar to the ash content (wt. %), and thus theresult of an ash test is used for quantification of the total mineralcontent in this disclosure.

Specific Ca, Mg, Na, and K contents were determined using a Perkin ElmerAtomic Absorption Spectrophotometer. Samples were treated withtrichloroacetic acid to precipitate proteins and the filtrate wasanalyzed by the Atomic Absorption Spectrophotometer. Phosphorus contentwas determined via Inductively Coupled Plasma Spectrometry (officialmethod of Analysis of AOAC, International 8^(th) edition, methods 965.17and 985.01). Chlorine content was determined by the official method ofanalysis of AOAC International 8th edition, methods 963.05, 972.27, and986.26; AOAC International, Gaithersburg, Md. (2005). Titratable acidity(%) was determined in accordance with American Public Health Associationmethod 15.021, 17th edition, Standard Method for the examination ofdairy product.

Tables I-VIII summarize composition information relating to thepreparation of yogurt products as described herein and illustrated inFIGS. 1-2. First, a raw or fresh milk product was separated into a skimmilk product and cream. The respective compositions of the raw milkproduct, skim milk product, and cream are summarized in Table I. Theskim milk product was subjected to ultrafiltration at a temperature ofapproximately 5° C. using a polymeric membrane system with a molecularweight cut-off of 10,000 Daltons, resulting in a yogurt base with higherprotein and solids; the composition of this yogurt base (UF skim milk)at a 6.6-6.8 pH is summarized in Table I and detailed in Table II.

The UF skim milk yogurt base was pasteurized at 88-92° C. for 6-8minutes, cooled to ˜40° C., and then inoculated with 0.004-0.009 wt. %of a yogurt culture containing Lactobacillus bulgaricus andStreptococcus thermophilus, and fermented at a temperature of ˜40° C.for 4-8 hours, at which time a pH of 4.4-4.6 was reached. Afteragitation and a thermization treatment at 55-60° C. for ˜3 minutes, thefermented product was subjected to ultrafiltration at 45-55° C. using aceramic membrane system with pore sizes of approximately 0.1 μm,resulting in a high protein, yogurt product (Skim Greek yogurt) with thecomposition summarized in Table I and detailed in Table VI.Substantially all (greater than 90 wt. %) of the acid whey was removedin the ceramic membrane ultrafiltration step, and the weight ratio ofthe yogurt product to acid whey in the fermented product wasapproximately 40:60. The composition of the acid whey (permeate) isdetailed in Table IV.

In a separate experiment, the UF skim milk product (protein-enriched)was combined with cream, resulting in a yogurt base with higher protein,fat, and solids; the composition of this yogurt base (UF skimmilk+cream) is summarized in Table I and detailed in Table III. The UFskim milk+cream yogurt base was then processed in a manner similar tothe UF skim milk yogurt base, described above. The resultant fermentedproduct was subjected to ultrafiltration using a ceramic membranesystem, resulting in a high protein, yogurt product (Whole Greek yogurt)with the composition summarized in Table I and detailed in Table VII.Substantially all (greater than 90 wt. %) of the acid whey was removedin the ultrafiltration step, and the weight ratio of the yogurt productto acid whey in the fermented product was approximately 50:50. Thecomposition of the acid whey (permeate) is detailed in Table V.

Constructive examples that demonstrate an unexpected benefit of thedisclosed methods are summarized in Table VIII, in which yogurt baseshaving different protein contents are listed (A=3.2 wt. %, B=4.46 wt. %,C=5 wt. %, D=6 wt. %). To produce a Greek-style yogurt product having atarget or nominal 10 wt. % protein content, the estimated amount of acidwhey (in kg) that would be produced per 100 kg of the yogurt product islisted in Table VIII for each yogurt base (and yogurt base proteincontent). Advantageously, increasing the protein content of the yogurtbase can dramatically decrease the amount of acid whey that is produced,and that must be disposed of. Note that an increase in yogurt baseprotein content from 3.2 to 5 wt. % (or from 4.46 to 6 wt. %) can reducethe amount of the acid whey by-product by 50%.

TABLE I Compositional Summary. Fat Protein Lactose Minerals SolidsTitratable Product Wt. % Wt. % Wt. % Wt. % Wt. % acidity (%) Raw milk3.5 3.2 4.8 0.70 12.2 0.12 Skim milk 0.07 3.3 4.9 0.75 8.9 0.13 Cream44.0 1.9 2.5 0.40 48.8 0.05 UF skim milk 0.17 4.2 4.6 0.96 10.1 0.11 UFskim milk + cream 2.14 4.8 4.3 1.04 12.2 0.12 Whole Greek yogurt 4.468.3 1.5 1.07 16.0 1.09 Skim Greek yogurt 0.28 9.6 1.7 1.28 13.8 1.12

TABLE II UF skim milk base - detailed composition. Component ResultMethod reference Fat (wt. %) 0.17 AOAC 989.05 Protein (wt. %) 4.15 AOAC992.23 Lactose (wt. %) 4.57 AOAC 980.13 Total solids (wt. %) 10.05 SMEDP15.10 C Chloride (wt. %) 0.10 AOAC 980.25 Titratable acidity (%) 0.11Calcium (per 100 g) 133 mg AOAC 984.27 Magnesium (per 100 g) 12.3 mgAOAC 984.27 Phosphorus (per 100 g) 94.0 mg AOAC 984.27 Potassium (per100 g) 151 mg AOAC 984.27 Sodium (per 100 g) 41.5 mg AOAC 984.27 Zinc(per 100 g) 0.44 mg AOAC 984.27 Calcium/protein 0.032 Phosphorus/protein0.023

TABLE III UF skim milk + cream base - detailed composition. ComponentResult Method reference Fat (wt. %) 2.14 AOAC 989.05 Protein (wt. %)4.78 AOAC 992.23 Lactose (wt. %) 4.31 AOAC 980.13 Total solids (wt. %)12.24 SMEDP 15.10 C Chloride (wt. %) 0.09 AOAC 980.25 Titratable acidity(%) 0.12 Calcium (per 100 g) 140 mg AOAC 984.27 Magnesium (per 100 g)12.5 mg AOAC 984.27 Phosphorus (per 100 g) 97.7 mg AOAC 984.27 Potassium(per 100 g) 144 mg AOAC 984.27 Sodium (per 100 g) 38.9 mg AOAC 984.27Zinc (per 100 g) 0.50 mg AOAC 984.27 Calcium/protein 0.029Phosphorus/protein 0.020

TABLE IV Acid whey (permeate) of Skim Greek yogurt - detailedcomposition. Component Result Method reference Fat (wt. %) 0.05 AOAC989.05 Protein (wt. %) 0.38 AOAC 992.23 Lactose (wt. %) 3.76 AOAC 980.13Total solids (wt. %) 6.16 USDA918 RL Chloride (wt. %) 0.11 AOAC 980.25Titratable acidity (%) 0.12 Calcium (per 100 g) 140 mg AOAC 984.27Magnesium (per 100 g) 13.1 mg AOAC 984.27 Phosphorus (per 100 g) 82.7 mgAOAC 984.27 Potassium (per 100 g) 171 mg AOAC 984.27 Sodium (per 100 g)46.3 mg AOAC 984.27 Zinc (per 100 g) 0.41 mg AOAC 984.27 As (wt. %) 0.83AOAC 945.46

TABLE V Acid whey (permeate) of Whole Greek yogurt - detailedcomposition. Component Result Method reference Fat (wt. %) 0.01 AOAC989.05 Protein (wt. %) 0.38 AOAC 992.23 Lactose (wt. %) 3.62 AOAC 980.13Total solids (wt. %) 5.95 USDA918 RL Chloride (wt. %) 0.09 AOAC 980.25Titratable acidity (%) 0.12 Calcium (per 100 g) 153 mg AOAC 984.27Magnesium (per 100 g) 12.5 mg AOAC 984.27 Phosphorus (per 100 g) 79.6 mgAOAC 984.27 Potassium (per 100 g) 174 mg AOAC 984.27 Sodium (per 100 g)44.3 mg AOAC 984.27 Zinc (per 100 g) 0.37 mg AOAC 984.27

TABLE VI Skim Greek yogurt - detailed composition. Component ResultMethod reference Fat (wt. %) 0.28 AOAC 989.05 Protein (wt. %) 9.57 AOAC992.23 Lactose (wt. %) 1.68 AOAC 980.13 Total solids (wt. %) 13.81USDA918 RL Titratable acidity (%) 1.12 Calcium (per 100 g) 95.9 mg AOAC984.27 Magnesium (per 100 g) 9.69 mg AOAC 984.27 Potassium (per 100 g)116 mg AOAC 984.27 Sodium (per 100 g) 32.5 mg AOAC 984.27 Lactic acidbacteria 2.4 billion per gram Calcium/protein 0.010

TABLE VII Whole Greek yogurt - detailed composition. Component ResultMethod reference Fat (wt. %) 4.46 AOAC 989.05 Protein (wt. %) 8.25 AOAC992.23 Lactose (wt. %) 1.52 AOAC 980.13 Total solids (wt. %) 16.02USDA918RL Titratable acidity (%) 1.09 Calcium (per 100 g) 90.6 mg AOAC984.27 Magnesium (per 100 g) 8.64 mg AOAC 984.27 Potassium (per 100 g)100 mg AOAC 984.27 Sodium (per 100 g) 30.7 mg AOAC 984.27 Lactic acidbacteria 1.7 billion per gram Calcium/protein 0.011

TABLE VIII Acid Whey Production. Yogurt Yogurt Yogurt Yogurt AttributeBase A Base B Base C Base D Yogurt Base 3.2 4.46 5 6 Protein (wt. %)Target Yogurt 10 10 10 10 Product Protein (wt. %) Acid whey (in kg) 220140 100 67 per 100 kg of Yogurt Product

1-20. (canceled)
 21. A method for making a yogurt product, the methodcomprising: (a) concentrating a skim milk product to produce aprotein-enriched milk fraction containing from about 3.5 to about 6 wt.% protein; wherein concentrating the skim milk product comprisesultrafiltering the skim milk product, microfiltering the skim milkproduct, nanofiltering the skim milk product, or subjecting the skimmilk product to reverse osmosis; (b) combining the protein-enriched milkfraction with an additional milk fraction comprising cream and/or skimmilk to produce a standardized yogurt base containing from about 3.5 toabout 6 wt. % protein; (c) inoculating the standardized yogurt base witha yogurt culture and fermenting the inoculated yogurt base to produce afermented product; and (d) removing at least a portion of acid whey fromthe fermented product to form the yogurt product.
 22. The method ofclaim 21, wherein the additional milk fraction comprises cream.
 23. Themethod of claim 22, wherein concentrating the skim milk productcomprises ultrafiltering the skim milk product.
 24. The method of claim22, wherein concentrating the skim milk product comprises microfilteringthe skim milk product.
 25. The method of claim 22, wherein concentratingthe skim milk product comprises nanofiltering the skim milk product orsubjecting the skim milk product to reverse osmosis.
 26. The method ofclaim 22, wherein removing in step (d) comprises ultrafiltering thefermented product.
 27. The method of claim 22, wherein removing in step(d) comprises microfiltering the fermented product or nanofiltering thefermented product.
 28. The method of claim 22, wherein the standardizedyogurt base contains: from about 3.8 to about 5.5 wt. % protein; fromabout 1100 to about 1800 ppm calcium; and from about 800 to about 1200ppm phosphorus.
 29. The method of claim 22, further comprising:pasteurizing the standardized yogurt base between step (b) and step (c);and combining the yogurt product in step (d) with an ingredient andpackaging in a container.
 30. The method of claim 21, wherein theadditional milk fraction comprises skim milk.
 31. The method of claim30, wherein concentrating the skim milk product in step (a) comprisesultrafiltering the skim milk product.
 32. The method of claim 30,wherein concentrating the skim milk product in step (a) comprisesmicrofiltering the skim milk product.
 33. The method of claim 30,wherein concentrating the skim milk product in step (a) comprisesnanofiltering the skim milk product or subjecting the skim milk productto reverse osmosis.
 34. The method of claim 30, wherein removing in step(d) comprises ultrafiltering the fermented product.
 35. The method ofclaim 30, wherein removing in step (d) comprises microfiltering thefermented product or nanofiltering the fermented product.
 36. The methodof claim 30, wherein the standardized yogurt base contains: from about3.8 to about 5.5 wt. % protein; from about 1100 to about 1800 ppmcalcium; and from about 800 to about 1200 ppm phosphorus.
 37. The methodof claim 30, further comprising: pasteurizing the standardized yogurtbase between step (b) and step (c); and combining the yogurt product instep (d) with an ingredient and packaging in a container.
 38. A methodfor making a yogurt product, the method comprising: (i) concentrating askim milk product to produce a standardized yogurt base containing fromabout 3.5 to about 6 wt. % protein and characterized by a weight ratioof calcium to protein in a range from about 0.02 to about 0.04 and aweight ratio of phosphorus to protein in a range from about 0.013 toabout 0.033; wherein concentrating the skim milk product comprisesultrafiltering the skim milk product or microfiltering the skim milkproduct; (ii) inoculating the standardized yogurt base with a yogurtculture and fermenting the inoculated yogurt base to produce a fermentedproduct; and (iii) removing at least a portion of acid whey from thefermented product to form the yogurt product.
 39. The method of claim38, wherein the standardized yogurt base contains from about 1100 toabout 1800 ppm calcium.
 40. The method of claim 38, wherein thestandardized yogurt base contains from about 800 to about 1200 ppmphosphorus.
 41. The method of claim 38, wherein removing in step (iii)comprises ultrafiltering the fermented product, microfiltering thefermented product, or nanofiltering the fermented product.
 42. Themethod of claim 38, wherein: the yogurt product contains from about 7 toabout 25 wt. % protein; from about 0.5 to about 3 wt. % lactose; andfrom about 10 to about 30 wt. % solids; and the yogurt product ischaracterized by a weight ratio of protein:lactose of greater than orequal to about 4:1.